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Pandemic H1N1 influenza virus discovered in elephant seals

Posted June 19, 2013

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New research suggests northern elephant seals can be asymptomatic carriers of the H1N1 influenza virus. (Photo by Trina Wood​)

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The 2009 H1N1 influenza virus that killed thousands of people worldwide was isolated in free-ranging northern elephant seals off the California coast a year after the pandemic began, according to a University of California-Davis study published May 15 in the online journal PLOS ONE.

It is the first report of the H1N1 viral strain in any marine mammal.

“We thought we might find influenza viruses, which have been found before in marine mammals, but we did not expect to find pandemic H1N1,” said Dr. Tracey Goldstein, lead study author and an associate professor with the UC-Davis One Health Institute and Wildlife Health Center. “This shows influenza viruses can move among species.”

UC-Davis researchers have been studying influenza viruses in wild birds and mammals since 2007 as part of the Centers of Excellence in Influenza Research and Surveillance program funded by the National Institutes of Health. The goal of this research is to understand how viruses emerge and move among animals and people.

Between 2009 and 2011, the team of scientists tested nasal swabs from more than 900 marine mammals from 10 species off the Pacific Coast from Alaska to California. They detected infection with the H1N1 influenza virus in two northern elephant seals and antibodies against the virus in an additional 28 elephant seals, indicating more widespread exposure.

Neither infected seal appeared to be ill, indicating marine mammals may be infected without showing clinical signs of illness. “Importantly, this work highlights that marine mammals may be infected with zoonotic pathogens and not show clinical signs of illness, thus being asymptomatic carriers,” the study states.

The findings are particularly pertinent to people who handle marine mammals, such as veterinarians and animal rescue and rehabilitation workers, Dr. Goldstein said. They are also a reminder of the importance of wearing personal protective gear when working around marine mammals, both to prevent workers’ exposure to diseases as well as to prevent the transmission of human diseases to animals.

The H1N1 influenza virus originated in pigs. It emerged in humans in 2009, spreading worldwide as a pandemic. The World Health Organization now considers the H1N1 strain from 2009 to be under control, taking on the behavior of a seasonal virus.

“H1N1 was circulating in humans in 2009,” Dr. Goldstein said. “The seals on land in early 2010 tested negative before they went to sea, but when they returned from sea in spring 2010, they tested positive. So the question is where did it come from?”

When elephant seals are at sea, they spend most of their time foraging in the northeast Pacific Ocean off the continental shelf, which makes direct contact with humans unlikely, according to the study.

The seals had been satellite tagged and tracked, so researchers knew exactly where they had been and when they arrived on the coast. Infections in both seals were detected within days of their return to land. Researchers believe exposure likely occurred in the seals before they reached land, either while at sea or upon entering the near-shore environment.